Soylent green is PEOPLE!!
Economists often get criticized for being obsessed about GDP. We are told (correctly, I might add) that income is not the be all and end all and that other things are equally if not more important.
However, what people often miss is the instrumental argument that economists often make, viz. that income is extremely highly correlated with these "other things" and makes an excellent simple summary statistic.
For a great example of this kind of argument, see Srinivasan, T.N., 1994, Human Development: A New Paradigm or Reinvention of the Wheel? American Economic Review 84(2): 238-243.
Or you could just check out the awesome graph that Justin Wolfers just made:
That's right people, the rank correlation between the UN's Human Development Index and good old income per capita is .95 (out of a maximum of 1.0).
GDP: It's not just for breakfast anymore!